Self-control is frequently defined behaviorally as a choice for a larger, delayed reinforcer over a smaller, more immediate reinforcer. Impulsivity is the converse of self-control and characterizes impulse disorders like drug abuse. An understanding of the factors that determine an individual's impulsive or self- control choices, and how drugs affect those choices, is crucial to the development of behavioral and pharmacological interventions for many behavioral disorders, including drug abuse. The purpose of this research proposal is to examine the effects of reinforcement magnitude and delay on drug taking using an established model of self-control. Rhesus monkeys working in a discrete-trials procedure will be allowed to self-administer different doses of a stimulant, cocaine (Experiment 1) or a depressant, methohexital (Experiment 2) with different sets of delays to drug infusion. A quantitative description of the data obtained in different drug reinforcement contexts will be possible and will allow examination of the self- control model for behavior maintained by drugs. Further, the experiments will examine the generality of findings from non-drug contexts. Such information has relevance to the understanding of choice in general, and ultimately to the potential development of treatments for, or prevention of, drug abuse.